As shown in FIG. 1, a conventional filter includes a raw water supply pipe (2), a processing water discharging pipe (7), a washing water supply pipe (6), a discharging pipe (1), and a filtering layer (4) formed of filtering materials. An air supply pipe (5) and a pressure adjusting and air discharging valve (8) are further provided for implementing an easier washing operation.
The operation of the above filter is divided into a filtering process and a washing process.
In the filtering process, raw water including a suspended substance is flowed into a filter for thereby producing processed water from which a suspended substance is filtered. In addition, in the filtering process, the pores formed in the filtering layer of the filter are directed to capturing the suspended substances in the raw water based on a complicated mechanism such as a mass separation, precipitation, inertia collision, blocking, absorption, cohesion methods for thereby producing a clean water as a processed water.
As the filtering process is continuously performed, the suspended substances are filled in the pores formed in the filtering layer, and the filtering resistance is increased. When the filtering resistance exceeds a certain degree, the filtering process is not performed. At this time, the washing is performed for eliminating the suspended substances filled in the pores by supplying a clean washing water and air. At this time, the performance of the filter is determined based on an eliminating ratio of the suspended substances, a filtering rate, a filtering duration time, the amount of a washing water, a washing frequency, a washing time, etc.
As the filtering materials that are filled into the filtering layer, there are known an inorganic granular material such as sand, anthracite, coal, etc. The above filtering materials may be easily obtained and are capable of filtering a particle smaller than the size of the pore formed by the filtering substances. However, in the filtering layer formed of the above filtering materials, since a filtering space for filtering the suspended materials is limited to a surface portion, the filtering resistance is fast increased due to the closed states of the pores. Therefore, the reverse-washing process must be frequently performed. In order to overcome the above problem in which the suspended substances are mainly captured in a surface portion, a filter in which a filtering layer is formed in a double layer or multiple layers is developed. In the above filter, filtering materials each having different granular diameters and densities are formed in each layer and the layers are not distinctly separated. Therefore, as the washing process is continuously performed, the boundaries between the neighboring layers are indefinite. Therefore, it is impossible to implement a desired purpose. In addition, when the granular filtering material is used, the filtering materials may be lost during the reverse-washing process.
Recently, according to a filter (Patent No. 10-0241198), in order to enhance the performance of the filter, a fiber material is used as a filtering material. In this case, a fiber material is fixed to a lower portion of the filter, and a raw water supply pressure pressurizes the filtering material, and the pressure of air and washing water expands the filtering material. According to the above filter, since a filtering layer is single, and the pressurizing degree of the filtering material is determined based on the supplying pressure of the raw water, the space for capturing the suspended substances is small, so that the filtering duration time is decreased, and the frequency of the washing operation is increased, and it is not easy to cope with the change of the quality of the flowing-in water. In addition, it is difficult to adjust the quality and amount of water. In order to overcome the above problems, a permanent type filter (Laid-open No. 1999-030247), which includes a variable type filter layer using a piston is developed. In the above filter, since the filtering material is pressurized and depressurized by the piston in the vertical direction, if the above filter is used for a long time, the filtering materials may be tangled, so that the filtering materials may not be fully recovered during the washing operation, and it is impossible to implement a desired washing operation.
In addition, according to a filter (Patent No. 1997-0007944), the filtering material is installed in a concentric shape between a movable circular plate and a fixed circular plate, and the movable circular plates are rotated for thereby pressurizing the filtering materials. However, the above filter has a disadvantage in that the filtering materials positioned near the circular plates are not pressurized, and the movable circular plate is moved in the direction of the fixed circular plate for thereby performing a pressurizing operation in order for the filtering material not to receive a tension force. In this case, the filtering area is too small compared to the size of a filtering tub (2). In addition, since the rotary shaft is moved through the filtering tub (2), it is impossible to implement a pressurizing filtering operation.